Control system for heaters



Jan. 7, 1936. 'r. A. WETZEL CONTROL SYSTEM FOR HEATERS Filed Dec. 29,1933 2 Sheets-Sheet 1 'INVENTOR. M 4%. 7 207; 2- 4.

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ATTORNEY} 1936- T. A. WETZEL v CONTROL SYSTEM FOR HEATERS Patented 1.....1, i936 UNITED STATES 2,026,720 V CONTBQ L SYSTEM FOR HEATERSTheodore'A. Wetzel, Wauwatosa, Wia, assignor to Automatic ProductsCompany,

Milwaukee,

Wis., a corporation of Wisconsin Application December 29, 1933, SerialNo. 704,369

8 Claim.

This invention relates in general to control systems called regulatorsfor use with heaters as, for example, hot air furnaces, hot waterheaters or similar types of heating plants.

Heretofore it has been customary to regulate the rate of combustion in aheater by means of a a room thermostat which controls the action of adamper regulator. The damper regulator con-- sists of an electric motorfunctioning to operate an actuating lever which acts through cables toopen and closethe direct draft and check drait dampers of the heater. Inaddition to regulating the-rate of combustion in the manner mentioned ithas also been proposed to regulate the the practice to use a furnacefan,which,when operating, forces a circulation of the hot air.

Such fans or their motors are controlled by means of a thermostaticswitch arrangementsubject to the temperature within the furnace andacting when such temperature rises to a predetermined value to turn thefan on and when the temperature in the heater drops below such value toturnthe fan off. These thermostatic switch arrangements are alsogenerally so constituted and combined in the system as to take thecontrol of the damper regulator away from the room thermostat should thetemperature within the heater exceed a limit consistent with safety.

The high limit temperature at which the fire is checked is predeterminedon the thermostatic switch arrangement and is reached only in the eventthat the fan is unable to cause the furnace temperature to drbp as thecool basement air is blown through the furnace. It is evident that whensuch a condition is brought about the fire has gained so much headway asto deliver heat at a faster rate than that at which the fan can carry itoff from the furnace. During the period in which combustion is beingaccelerated the fan will periodically operate for short intervals afterthe fire has come up from a cold start. First, when the fan switchtemperature setting is reached within the furnace hood the fan startsoperating and continues for only a short period since at such time noprolonged acof the heater is such as to result in the dampers beingclosed and acceleration ofcombustion, checked.

The present invention proposes to modify a system of this character byintroducing thereinto a control in the nature of a time limit switchwhich functions to close the dampers after the fan motor has operatedfor a selected period. The time required for the operation of such timelimit switch will, of course, be variable and adapted to the conditionsobtaining in any particular installation but will preclude such undueacceleration of combustion as would result from the operation of thepresent high limit safety switch. As a result substantial economy in theconsumption of fuel and the uniform and 15 more desirable operation ofthe heating plant is had.

Another object of the invention residesin the provision of a controlsystem of this character which is simple and durable in construction,ca-

pable of being readily'and conveniently installed and reliable, safe andeflicientdn operation.

Other objects and advantages reside in certain novel features of theconstruction, arrangement and combination of parts which will behereinafter more fully described and particularly pointed out in theappended claims, reference being had to the accompanying drawings,forminga part of this specification, and in which:

Figure 1 is a diagrammatic view showing one type of heat regulatingsystem to which the present invention is applicable; and

Figure 2 is a diagrammatic view illustrating one manner of combining thecontrol features of the present invention in a system of this character.

Referring to the drawings, and more particularly to Figure 1, it will beseen that in the em.- bodiment of the invention illustrated, the controlsystem has been shown applied to a hot air furnace. It is to beunderstood that the invention is not restricted to this particular typeof heating plant and that this type is shown merely for the sake ofsimplicity in illustration.

The hot air furnace is designated generally at l and is equipped withthe usual direct draft damper 2 and check draft damper 3. It is alsoprovided with an air conditioner or fan 4 driven in the usual way by anelectric motor indicated diagrammatically at 4' in Figure 2. The fan 4,when running, forces air from the basement up through the hood 5 of thefurnace and out through the usual hot air pipes (not shown).

Dampers 2 and 3 are connected by means of cables l0 and H with the crankarm or operating lever ll of a damper regulatordesignated gen- 56 erallyat l5. the cables being guided about suitable pulleys l2 and I3. It willbe understood that the arm I 4 of the regulator is geared in anysuitable way to an electric motor embodied in the regulator andindicated diagrammatically at l1 in Figure 2. Such an electric motor isusually an induction motor of the shaded coil type.

For controlling the operation of the damper regulator and the furnacefan or blower 4, control instrumentalities comprising generally a roomthermostat l3, a furnace fan thermostat l9 and a time limit switch 23are provided, which instrumentalities are connected up with, the otherelements of the system in the manner illustrated in Figure 2 and whichwill now be described.

A control box 22 containsthe elements of the electrical system exceptthose embodied in the draft regulator l5, room thermostat, l3 andfurnace fan thermostatic switch l9.

As shown diagrammatically in Figure 2, the room thermostat |3 is ofconventional construction and comprises the so-called blue and "red"contacts 25 and 26 between which a switch blade 23 operates. g

The damper regulator I5 is also conventional and has associatedtherewith switches 29 and 33 having fixed contacts 3| and 32 and movablecontacts 33 and 34, respectively. The movement of the contacts are onthe opposite sides of an operating member 35 which is rotated insynchronism with the motor of the damper regulator to alternately openand close these switches 29 and 33 and thereby stop the operation of themotor after the completion of such movement thereof as will effectopening or closing of the dampers. This switch arrangement is a wellknown expedient.

Power lines (not shown) are connected to the terminals 36 and 31 of thecontrol box 22, as illustrated diagrammatically in Figure 2. Theterminal 36 is connected by wires 33 and 33 to one end of the primarycoil 43-of a transformer designated generally .at 4|, whereas the otherend of this transformer coil is connected by a wire 42 with the terminal31. The secondary coil of the transformer 4| is designated at 43 and oneend thereof connects by a wire 44 with the so-called red contact 26 ofthe room thermostat. A wire 45 has one end connected to the wire 44 andhas its other end connected to a wire 46 which connects up with thefixed contact 32 of the switch 33. The other end of the secondary coilof the transformer is connected by a wire 41 with the winding of themotor 11 of the draft regulator. The other end of this motor winding isconnected by means of a wire 43 with a wire 49, one end of which wire 49is connected to the fixed contact 3| of the switch 29, whereas the otherend of this wire 49 is connected with the so-called blue" contact 25 ofthe room thermostat. The switch blade 23 of the room thermostat connectsby means of a wire 53 with the winter contact 5| of the summer-winterswitch. The adjacent fixed contact 52 of this summer-winter switch isconnected by means of a wire 53 with the wire 49. As shown in Figure 2,the movable contact 54 of the summer-winter switch is engaged with thefixed contact 5|, and it, in turn, is connected by means of wire 55 withone of the fixed contacts 51 of the time limit switch 23.

The time limit switch 23 has a shiftable blade contact 53 which connectsby a wire 59 with the shiftable contact 33 of the switch 29. A flexiblewire 63 also connects this wire 53 with the shifts.-

ble contact 34 of the switch 33.

The time limit switch 23 also has a second fixed contact 6| connected bya wire 62 with the wire 49. A continuation 63' of this wire 62 connectswith one of the fixed contacts 63 of the thermostatically operated fancontrol switch I3. The

other fixed contact 64 of this switch |9 connects by a wire 65 with thewire 55. The movable contact 66 of the fan control switch I9, operatedby a thermostatic element 66' positioned in the hood of the furnace, isconnected by means of a wire 61 with the movable blade 63 of a switch 69em: bodied in a relay 13. The fixed contact 1| of this switch 69 isconnected by a wire 12 with the return wire 41. The wire 61 is alsoconnected with a wire 13 which leads to a fixed contact 14 of thesummer-winter switch. A movable contact 15 of this summer-winter switchconnects by means of a wire 16 with one end of a relay coil 13, whereasthe other end of this coil 13 connects by means of a wire 19 with thewire 53. It will be noted that the fourth fixed contact 33 of thesummer-winter switch connects by means of a wire 3| with the wire 45.The relay coil 13, when energized, not only closes the switch 69 butalso closes the switch 32 incorporated in the circuit provided for thefan motor 4'. It will be noted that a wire 33 connects the terminal 36with one of the motor terminals 34 of fan motor 4. The other motorterminal is connected by means of a wire 36 with the movable contact 31of the switch 32. The fixed contact 33 of this switch 32 is connected bymeans of a wire 39 with the other terminal 31. It will be appreciatedthat with the switch 32 closed the fan motor is energized whereasopening of the switch 32 stops the motor 4'. It will further beappreciated that the relay coil 13 must be energized to effect closureof the switch 32.

- The time limit control switch 23 has a bimetallic strip for itsmovable contact 53 and in operative relation to this strip 53 is aheating element 93 which is connected by means of wires 9| and 92 acrossthe fan motor circuit so that when the fan is running current will flowthrough the electric heating. element and should the fan run long enoughor its periods of operation be' closely connected in time of sequence,i. e., frequency of operation is greater, this element will heat thestrip 53 to such extent as to cause'it to flex away from the fixedcontact 51 and into engagement with the fixed contact 6|. Snap action ofthis movable contactor strip 53 may be had by the utilization ofpermanent magnets 93, as illustrated in Figure 7 2. The fan controlswitch I9 may also be provided with a similar permanent magnet 95 for asimilar purpose.

With the parts positioned as shown in Figure 2, the room thermostat issatisfied and the fan motor circuitis opened. If now the roomtemperature drops below the setting of'the room thermostat the bladecontact 23 will shift over into engagement with the red contact 26 withthe result that the motor ll of the draft regulator will be energized tocause opening of the direct and closing of the check draft dampers. Atsuch time current flows from the secondary coil of the transformer,through wire 44, contacts 26, 23,-wire 53, contacts 5| and 54, wires and56, contacts 51 and 53, wire 59, contacts 33 and 3|, wires 49 and 43, tothe winding of the motor and thence through the winding and back throughthe return wire 41 to the other end of the secondary coil of thetransformer 4|. When the motor has completed the opening of the directand the closing of the check draft dampping the flow of current throughthe motor II of the draft regulator upon satisfaction of. the roomthermostatandreturn ofits contact 28 into engagement with the contact28. The

dampers being opened, combustion in the, furname is accelerated and thetemperature in the hood of the furnace rises until eventually a pointrelay coil 18, the current flowing from the secondary of the transformer4| through the wire 44, contacts 28 and 28, wire 88, wire 18, coil I8,wire I8, contacts 18 and 14, wires 18 and 81, contacts 88 and 88, wires82, 48, 48, winding of motor l1, and return wire 41, back to the otherside of the transformer secondary. In the cir- "'cuit just describedthemotor l1 and relay coil I8 are in series on the low voltage side of thetransformer and the coil I8 will be energized sufficiently to lock '01close the low voltage contacts88,.'|l without operating the motor. Theenergizing of coil '18- also closes the fan motor switch 82. -It will beunderstood that as the low voltage contacts 88, II- of the relay arelocked, the draft regulator motor is shorted out of series, the currentflowing as described above till wire I8 is passed then instead offlowing as thus described it, will pass to wire-82, contacts 88 and II,wire 12 and return wire 41 to the secondary. The coil I8 will then takethe full current which prevents the contacts 88, II from chattering andthe regulator motor from running except when the time limit switch 28,fan switch I! or the room thermostat l8 call for check. In such event,the relay is unlocked by an instantaneous short on the transformersecondary which is broken at the low voltage contact on the relaythereby allowing the relay to open so that the draft regulator motor maythen start and complete its cycle. In the last circuit described thecurrent was flowing from the secondarythrough the wire .44, contacts 28and 28, wire 88, wire 18, coil 18, wire 18, contacts 18 and 14, wires 18and 82', contacts 88 and II, wires Hand 41 back to the secondary.However, the time limit switch was in the position where contacts 58and. 81 were connected, the fan control switch in the position wherecontacts 88 and 88 were connected and the regulator motor switch tacts88, II will open. If the fan switch is changed so that contacts 88 and84 are connected thecurrent will flow from the secondary through wire44, contacts 28 and 28, wire 88, contacts SI and 54, wires 85 and 88,contacts 84 and 88, wires 81 and 82., contacts 88 and II, wires 12- and41 and back to the secondary. Coil I8 is not included in this circuitand will become acunae more switch =20 will be opened thereby:stoptie-energized. n thermostat is changed so that contacts 28 and 28are connected the current willflow from the secondary through wires 44,48 and 48, contacts 82 and 84, wires 88 and 88, contacts "and 81, wires88 and;58, contacts 84 and 8!, wire 88, contacts 28 and28,

back to thesecondary. Coil "is not included 7 in-this,circuit'. Hence,if one of the three is reached where the :hood temperature-is efchangesmentioned is madepwhilethefan is running and coil 18 is energized, thecoil will be shorted out of its circuit. with the secondary, becomede-energizedthereby permitting the switches 88 and 82 to open. Operationof the fan lowers the temperature of the hood of the 'furnace and at thebeginning of acceleration of combustion does not require much time toaccomplish this. Upon a predetermined drop,

the blade 88, under the influence of its thermostat, shifts over intoengagement with the contact 84 whereby the coil 18 is tie-energized withconsequent opening of the switch 82 and stop ping of the fan. As thecombustion continues to accelerate the fan periodically turns on andofl, the time interval between the stopping and starting of the fandecreasesandmore and more time is required each time the fan turns on topull down the temperature in the furnace hood. A point will be reachedin which the heat of the heating element 88 caused by the fan operationwill not be entirely dissipated beforethe next per'od of fan operation.Because of this characteristic any increase of acceleration in the rateof combustion will cause an earlier shifting of the time limit switchand before the rate of combustio'n has advanced to a-point where moreheat would be produced than the fan could emciently distribute, theelectric heating element 88 will become so heated up as tov cause thebismetallic strip 58 of the time limit switch to shift over intoengagement with the fixed contact 8| thereby causing the draft regulatorto move the dampers to check the furnace, notwithstanding the roomthermostat still calls for heat. At such time, current flows from thesecondary of the transformer through the wires 44 and 48, to thecontacts 82 and 84, thence through the flexible wire 88, to wire 88.thence through contacts 58 and 8| to wire 82 and from wire 82 throughwires 48 and 48, coil I'I, wire 41 back to the other end of thissecondary of the transformer. During the operation of the draftregulator motor, the fan, if operating, will be momentarily stopped, butif the hood temperature is still so high as to maintain contacts 88 and83 engaged, fan operation will be resumed upon the completion of thedamper movement. This will result in the electric heating element 88being further heated and continuing the engagement of the bi-metallicstrip 88with the contact 8|. However, when the hood temperature dropsbelow the selected point and thecontacts 88 and dampers.

The summer-winter switch has two movable blades 54 and 18 which aremoved simultaneously by hand from respective connection with contacts 8|and 14 to respective connection with contacts 52 and 88, this latterposition being the summer position. When in this position the drafts arealways closed and the motor regulator switch and Ian control switch.remain in the po- 5 sitionsshown in Figure 2. When the room. temperatureis below a set degree the'contacts 28 and 26 are connected and thesecondary-will beon an open circuit which means that the fan motorswitch 82 will be open. When the. room temperature rises above that' setdegree the contacts 28 and Here connected-and the'current will flow fromthe secondary through'wir'es 44, 45, and BI, contacts 88 and I5;wire-16, coil 18, wires 9 and 50, contacts "and 25; wires 48 and 48,motor i l wire -41 back to the secondary 43. Thus,- motor I! coil 18will be in series wzm the secondary and coil 18 will be energizedclosingthe fan switch 82 and low voltage switch '69 without operating themotor. As soon as the 20 low voltage switch 69 is closed the currentwill flow as above until wire 49 is reached and then it will branch offthrough wire 53, contacts '52 and 54, wires 55 and 65, contacts 64 and66,

wires 61 and 62', contacts 68 and 1|, wires 12 and 41 to the secondary.The coil 18 will then take all the current of the secondary and securelylock the switches 82 and 69 in closed position.

The fan will blow air through the system but since there is no firetheair will have a cooling effect. The time limit switch has no controlunder the summer circuit hence the fan will continue to operate untilthe room temperature is lowered and the contacts 28 and 26 are movedtogether breaking the entire circuit and stopping the fan.

While I have shown and described one control system and construction inwhich the invention may be advantageously embodied, it is to beunderstood that such has been selected merely for the purpose ofillustration or example and that various changes, as will be obvious toone skilled in the art, may be made without departing from the spirit ofthe invention or the scope of the subjoined claims. The inventionclaimed is:

1. A heater control comprising a damper, a

fan for circulating air through the heater, a

damper regulator, a room thermostat controlling the' damper regulator, athermostatic switch controlling the action of the fan, and a time limitswitch subject to the influence of fan operation and exercising adominant control over the damper for closing the same when the fan, isoperated for a predetermined period.

2. A heater control having means for regulating the rate of combustion,means for controlling the supply of a heat conducting medium,thermostatic means for regulating the action of the aforesaid means, anda time limit switch regulated in its action by said second-named meansand exerting a dominant control over the firstnamed means after thesecond-named means has operated for a predetermined time.

3. A heater control having means for regulating the rate of combustion,means for controlling the supply of heat conducting medium, elec# tricalthermostatic means for regulating the action of the aforesaid means anda time limit switch including a heating element energized when saidsecond-named means is in operation,

a bi-metallic switch element influenced by said heating means andcontacts with which said bi-metallic element alternately cooperates.said contacts and said bi-metallic switch element being associated withsaid thermostatic electrical means whereby the time limit switch exertsa dominant control over the first-named means after .the second-namedmeans is operated tor 5 a predetermined time.

4. A. heater control comprising a damper, a damper regulator having anelectric motor ror operating the same, a circuit for said motor, a roomthermostat incorporated insaid circuit and 10 normally regulating theopening: and closing thereof; a 'tanfor iorcing the circulation "of airthrough said heater, an'electric motor for oper-'- ating said fan, acircuit for said fan motor interrelated with the circuit for thefirst-named 15 motor, a switch in said fan motor circuit, a thermostatsubject to the heater temperature for opening and closing said switch,and a time limit switch incorporated in the circuit for the firstnamedmotor and subject to the influence oi the 20 circuit for thesecond-named motor for closing said damper upon operation of said fanfor a predetermined period. i

5. A heater control comprising a damper, a

damper regulator therefor, a room thermostat 5 controlling saidregulator, a motor operated fan for enforcing air through the heater, 9.thermostatic switchsubject to the heater temperature for regulating theoperation of the fan, and a time limit switch controlled in its actionby the 30 fan operation and exerting a dominant control over the damperregulator when the fan has operated for a predetermined period.

6. A heater control comprising a damper, a damper regulator having anelectric motor for 35 operating the same, a. circuit for said motor, aroom thermostat incorporated in said circuit and normally regulating theopening and closing thereof, a fan for forcing the circulation of. airthrough said heater, an electric motor for operating said fan, a circuitfor said fan motor inter-related with the circuit for the first-namedmotor, a switch in said fan motor circuit, a thermostat subject to theheater temperature for opening and closing said switch, and a time 45limit switch including fixed contacts and a shiftable bi-metalliccontact incorporated in the circuit for the first-named motor and alsoincluding a heating element incorporated in the fan motor circuitwhereby to leave the control of the 50 damper regulator motor to theroom thermostat except after operation of the fan for a predeterminedperiod.

7. A heater control having means for regulat ing the rate of combustion,means for controlling 55 the supply of a heat conducting medium, andmeans related with said second-named means for exercising a dominantcontrol over said firstnamed means, said last-named means being directlyinfluenced by said second-named means 60 to exercise said dominantcontrol.

8. In a heater control, means for regulating the rate of combustion,means operating to control a supply of a heat conducting medium,thermostatic means responsive to heater temperature and preventing saidsecond-named means from operating when said heater temperature is belowa predetermined degree and means utilizing the length and frequency ofthe time of operation of said second-named means and related with saidsecond-named means to exercise a dominant control over said first-namedmeans.

THEODORE A. WETZEL.

